Process for casting films



1955 3 Sheets-Sheet l 1N VENTOR. W

c. SCOTT PROCESS FOR CASTING FILMS Filed July 25,

March 14; 1939.

Mmh '14, 1939. c. SCOTT 2,150,250

PROCESS FOR CASTING FILMS Filed July 25, 1955 5 Sheets-Sheet 2 7/ K 33 m3a 2a 4 Z5 INVENTOR.

March 14, 1939. C COTT 2,150,250

v PROCESS FOR CASTING FILMS Filed July 25, 19:55- 3 Sheets-Sheet 3INVENTOR.

Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE PROCESS FOR. CASTINGFILMS Clyde Scott,East Orange, N. J. Application-July 25, 1935, SerialNo. 33,000

14 Claims.

This is a continuation in part of my application, Serial Number 666,358,filed April 15, 1933, for Process and apparatus for casting film's.

The invention to which the following description relates deals withimprovements in methods and apparatus for continuously casting film insheet or strip form from solutions of cellulose such as nitrocellulose,acetylcellulose, cellulose ether, or like material. I have found thatthe film is improved and its production facilitated by maintaining anaccurate and close control of the conditions under which the operationis carried out. Furthermore, this controlling operationis facilitated byimprovements in the mechanism relating to the casting operation, thesurfaces upon which the film is deposited and the subsequent operationsby which the film is produced in final form.

In the rapid production of film it has been found that the successfulapplication of currents of warm air or other evaporating media to thefilm during its conditioning, has necessitated the use of high-boilingsolvents or mixed solvents containing high-boiling components and thatthis presents a difficulty in the tendency of the newly deposited filmsto ripple, wrinkle or web when brought into contact with suchevaporating currents.

It. is an object of my invention to make possible the use of lessexpensive low-boiling solvents through the establishment'of a quiescentatmosphere. In this manner it is even possible to add to theselowboiling solvents considerable quantities of diluents withoutdeterioration of the desirable qualities in the film so formed. As anexample, the evaporation of a cellulose acetate film may be carried outsuccessfully in a quiescent atmosphere of solvent vapors in whichlowboiling acetone is the dominant solvent although mixed or dilutedwith as much as 50% of its weight of benzol.

It is characteristic of many cellulose ester or ether solutions thattheir viscosity may be varied and controlled by mechanical treatmentalone. As an incident of my invention I have prepared highlyconcentrated cellulosic solutions by such forms of treatment as heating,agitation and filtration while hot in order that the solution may bepurified, rendered uniform throughout and its viscosity sufiicientlydiminished to permit satisfactory deposit in the form of extremely thinfilms of desired predetermined thickness.

In order to obtain highly concentrated cellulose solutions particularlyof cellulose acetate, acetone or solvents such as the like which have anatural tendency to lower the viscosity of such solutions may besupplemented with heat to obtain fluent solutions containing a higherconcentration of solids than would otherwise be possible.

The working temperature of solutions and 5 apparatus is important.Diffusion in cellulosic solutions is ordinarily a very slow process, butis accelerated by rise of temperature. A homogeneous solution remains soonly as long as the different portions are maintained at the same tem-10 perature. When one portion of an initially homogeneous solution iskept at a different temperature from the other portions the solutionbecomes heterogeneous, the colder portion becoming more cencentratedthan the warmer part, 15 while dissolved substance tends to diffuse fromthe warmer into the colder zone of the solution.

The viscosity of cellulose nitrate solutions is a very importantproperty, especially so in solutions adapted for film-forming by castingand evapo- 20 rating processes. Great variations are noted in thesesolutions with changingtemperatures. Viscosity is related tomolecularcomplexity, and there is no doubt that in solutions of high viscositythe molecular complexes are comparatively 25 large. It is possible totrace a direct connection between the viscosity of such solutions andthe mechanical and chemical treatments to which they have beensubjected. The viscosities are diminished by treatment which thesubstance or 3 its raw material undergoes, such as heating the mixtureand heating the finished cellulosic solution.

My herein described process permits of a wider range or scope of formingfilms by casting and evaporating methods than is possible by othermeans. For example, whenan endless belt or drum is employed theviscosity of the film-forming component must permit of great fluidity.The solvents must be sufiiciently volatile to per- 40 mit the depositedsolution to set quickly and the resultant film to be stripped off orremoved from the casting-surface before one complete cycle of thecasting-surface has been made. In heretofore proposed apparatus andprocesses the filmforming solutions are deposited upon supports havingan even, close or polished surface to which the film, when fully dried,will not adhere. It is, as a rule, deposited upon the casting-surface towithin about one or two inches from the edges of the support and upondrying, the film immediately leaves or separates from thecasting-surface (particularly at the edges), due to lack of adhesion.Films produced by endless-belt, or drum apparatus are usually ofdimensions of from 0.003 to 0.007 or 0.008 of an inch thick. The greatdifiiculty of producing and stripping thinner films, due to theseparation from the casting-surface at the edges, prevents thesatisfactory production of films thinner than 0.003 of an inch inthickness. Obviously very heavy gauge thick films cannot be produced bysuch means in continuous operation even though a plurality of means beprovided as has been proposed for depositing successive layers,primarily on account of the limited area available for drying purposes.

The method of applying the solution to the casting surface in-a poolfrom which the film is withdrawn permits the solution to come in contactwith the guide-strips at the side for an extent many times greater thanthe thickness of the final film. The result is that this wetting of theguide-strips by the solution forms an extended attaching edge withgreatly increased adhesion. This bond with the guide-strips remains,during the drying and subsequent treatment of the film. on the castingsurface. It follows that there is an improved holding effect whichmaintains the film under tension, fiat against the surface of thecasting surface. This permits complete drying without danger of curlingand successive coating solutions may be applied without impairing theuniformity of the film or distorting it.

Because of the ability of the guide-guard strips on my machine to retainthoroughly dried films (and particularly very'thin and very thick films)in intimate contact with and upon the plane surface of thetravelling-supports, it becomes possible to cast very thin multi-layerlaminae i. e., composite films of one to two one-thousandths of an inchthick and dry under ten.- sion each successive layer without the filmsseparating from the support at the edges, and without substantialdistortion, wrinkling, warping or curling of the film during the processof manufacture or after removal from the casting-surface.

In the depositing of this film I have provided an improved dischargehopper by which the solution is first maintained in the proper conditionof low viscosity and then delivered in accurately measured quantities asis desired in order to produce a suitable film.

Among the objects of my invention is the provision of an improvedcasting surface which is mechanically advanced past the above mentionedhopper. In the use of this casting-surface it is maintained at theproper temperature in conformity with the temperature of the solution sothat the evaporation of the film will not be disturbed by localtemperature changes which might cloud the film or produce irregularitiesor blemishes therein.

Another object of my invention to provide improved means in the form of.guide strips by which substantially the full surface area of thecasting-surface is rnade available for the film and the necessity oftrimming wastage from the latter is minimized to a great extent.

As an incident of this object of my invention it is to be noted that thedevice provides means by which the film, when once cast on the surface,is held rigidly in place without distortion, warping or curling and maythus be subsequent ly treated by the deposition of successive layers ofsimilar or dissimilar material thereon.

Among the further objects of my invention is the completion of thefilm-forming operation by subjecting the solution'when cast to travelalong an upward gradient opposite to the direction in which the solutionis first applied, in an atmosphere of the solvent used in the film andkept at a degree of saturation and moderate temperature that will permitthe evaporation of the film in the most effective and prompt manner.

The film produced by this invention may be the subject of a furthersuccessive deposition by which its Water-proof, moisture-proof orfireproof properties will be improved or modified. As a final step theinvention contemplates the conditioning of the film as a continuousstrip or in shortened sections in a conditioning chamber.

In order to illustrate one preferred form which my invention may take,the following drawings are shown for the purpose of example only of amachine by which the above and other related objects may besatisfactorily attained. In the drawings Fig. 1 is a top plan view ofthe improved machine;

Fig. 2 is a side elevation thereof;

Fig. 3 is a side elevation showing the adjustment in inclination of thecasting machine;

Fig. 4 is an end elevation;

Fig. 5 is a top plan View of the improved hopper.

Fig. 6 is a side elevation thereof;

Fig. 7 is an end elevation of the same;

Fig. 8 is a vertical section on the line 8-8 of Fig. 6;

Fig. 9 is an enlarged transverse detailed section of the casting elementand associated parts;

Fig. 10 is an enlarged view of the hopper discharge shown in Fig. 8;

Fig. 11 is a fragmentary detail side View of the casting plate and itsmounting and Fig. 12 is a longitudinal section of the casting surfacedrive means.

The casting machine consists generally of a device for advancing aseries of casting plates to form a continuous surface on which thecellulose solution or the like may be deposited and subsequentlytreated. In the drawings this machine is shown to consist in a stand ortable II having at one end a pair of trunnions 12. Between thesetrunnions I? there is a table which extends for the full length of thestand I I. table I3 is supported at the other end of the stand by meansof a pair of standards I l which are locked in adjusted position to thestand H.

A cross bar I5 at this end of the stand forms a journal for the liftingscrew l6, one end of which is manipulated by the hand wheel H. The upperend of the lifting screw it supports the cross bar l8 beneath the table13 and serves to lift the latter to give it any desired inclination orgradient. In this way the left or discharge end of the table i3 israised relatively to the opposite end an amount dependent upon theoperating factors ofthe casting machine such as the viscosity of thematerial, the rate of travel of the casting-surface and the rate ofevaporation.

The table l3 has a series of transverse shafts H) which carry a pair ofparallel spaced endless conveyor chains 20, 20 by means of appropriatesprocket-wheels. or the like. This may form one endless conveyorconnecting the opposite ends of the table 13 or the conveyors may bearranged in overlapping relation serving successive zones along thetable and delivering the casting plates from one conveyor or zone toanother. One of the transverse shafts I9 is provided with a driven wheel2| by which the conveyor or series of conveyors is causedto operate. Theconveyor chains 2|] are provided at appropriate distances withengagement pins 22 by which the casting plates are I advanced along thelength of the table.

The casting plates consist of polished glass or metal plates 23 whichrest at their side edges on appropriate tracks or shoes and are advancedby means of transverse metal bars 24 also resting upon the shoes andbeing engaged by the pins 22. As is shown in the drawings the metal bars24 are of substantially the same thickness as the glass casting platesbut are undercut or rabbeted along one edge to accommodate the pins 22.The lengths'of the plates 23 and bars 24 are such as to provide acontinuous top surface upon which the solution may be cast or caused toflow.

In those instances where it is feasible and desirable to use a metalcasting plate it may take the form of a plate similar to the glass plate23 except that the opposite ends are rabbeted to accommodate the pins22.

Referring to Fig. 9 it will be seen that the casting plate 25 is urgedin a forward direction by the pins 22. The plate rests upon anaccurately proportioned shoe or track 21 which in turn is mounted on theside member of the table I3.

The table l3 also carries along its upper side edge a curbing 28 andabove that an inwardly extending flange 29. This flange begins inadvance of the point where the solution is deposited on thecasting-surface and. may continue into the subsequent zone ofevaporation.

A guard strip 30 having a U-shaped cross-section is provided to becarried along the side edges of the casting plate 25. This guard strip30 fits snugly against the side wall of the curbing 28 but there issuflicient vertical clearance between the flange 29 and the side memberof the table I3 to prevent the guard strip from binding against eitherthe flange or the side member of the table and the overlap of the strip30 with the side edges of the casting plate 23 compensates forvariations in the horizontal direction.

These guard strips 38 are of the same length as the individual castingplates 25 and travel with the plates from the point of their placementon the conveyor to the opposite end of the machine.

The vertical adjustment of the shoe or track 21 insures a straight lineof travel for the casting plates while the curbings 28 prevent lateralmovement of the plates.

The casting operation is carried out along a portion of the table l3which is equipped with a suitable cover to form a chamber for thesolvent vapors. As illustrated in Figs. 1 and 2 this chamber comprisespanels 32 which latter extend along the sides, ends and top of the frameto form a relatively closed chamber 33. Panels 32 are illustrated asbeing of framed sheet glass sothat the casting operation can be observedreadily. The ends of the chamber 33 are open at the bottom sufiicientlyto permit the introduction and withdrawal of the casting plates orsimilar elements without substantial loss of the solvent vapors or theproduction of undesirable air currents.

The chamber 33 is provided with suitable means, not illustrated, for itstemperature control and for the withdrawal of excess vapors producedfrom the evaporation of the film solution. In this way these vapors arerecovered and the solvent made available for use again while the ratedryer or other device by which the film is further and finally treated.

In the delivery of the film from the chamber 33 it may pass as acontinuous strip or web or may be cut into pieces of the desired length.In the latter case the sections of the casting surface will be made ofthe selected length so that the individual sections of the castingsurface together with the film deposited thereon will be 7 transferredto the chamber 34.

One standard 35 is bolted or otherwise attachedto each side member l3 ofthe frame and extends upwardly within and above the chamber 33. Thesestandards provide guides and supports for the casting hopper 36. Thishopper includes a pair of end walls 31 and a rear wall 38. The end walls31 have yokes 39 by which the hopper is slidingly held by thestandards35. Each end wall 31 has bolted thereon a bar 48 which extendsbeyond the front of the end wall 31 and has a rearward extension 4|.This extension 4| is screwthreaded at the point'which overlies the endof the standard 35. The extreme end of the extension 4| carries a gauge42.

Vertically extending through each extension 4| is an adjustment screw 43the lower end of which rests upon a bearing in the end of the standard35. The upper end of the adjustment screw 43 carries a handwheel 44 theedge of which is calibrated.

The adjustment screw 43 supports the weight of the hopper and its loadon the ends of the standards 35 and the hopper is prevented frommovement in any but a vertical direction by means of the yokes or guides39. The spacing of the hopper with respect to the casting-surface isindicated by the gauge 42 and the calibration of the handwheels 44 sothat a close control can be made of each end of the hopper and a uniformspacing for the casting film thus maintained.

The top 45 of the hopper has an opening 46 through which the inlet 41 ofthe film solution projects.

The top 45 also supports a heating coil 48 the convolutions of whichextend generally through the body of the film solution and serve tomaintain it at such a degree of temperature as will lower its viscosityand control the conditions under which the solution will be deliveredwith greatest efiectiveness. The back wall 49 of the hopper is formed ofa panel which is hinged at the top and the lower end is free to moveinwardly with respect to the rear wall 38.- The rear wall 38 has adepositing lip 58 toward which a corresponding lip 5| on the back wall49 is adapted to be spaced, both lips serving to reinforce the sheetmetal walls 38 and 4|]. In this way a delivery slot is establishedthrough which a thin stream of the film solution passes to thecasting-surface.

' The upper edge of the wall 49 has two or more hinged brackets 52 bywhich the wall is suspended .pivotally :on the cross bar 53. The crossbar, in turn, is freely journalled in bars 54 on the ends .31 andcarries calibrated dials 55. The free ends of the brackets 52 .areapertured to carry adjustment screws 55. The heads of the screws 56 restupon the free ends of the brackets 52 and carry operating levers 51. Thelower ends of the screws 55 pass through screw-threaded openings in. abar 58 which in turn extends transversely of the hopper between the bars43. In this way the adjustment of the screws 56 will cause the wall 49and the lip 5| to vary the size of the discharge slot. When operatingcircumstances demand, an operating handle 59 mounted on wall 59 may beused to move the latter inwardly until the discharge slot is entirelyclosed. It is to be understood that the side edges of the wall 49 willcome in such close contact with the end walls 3'! of the hopper as toprevent undesirable discharge of the solution at these points.

It is not intended primarily that the discharge from the hopper willcontrol directly the operation of depositing the film but mainly willserve as a feeder for the solution. The solution pass-- ing from thehopper flows backwardly and forms a slight pool on the casting-surface:due to the upward slope of the latter. The deep end of the pool isformed by a baffle 60 which extends in front of the feeding lips 56, 51and for the full width of the hopper of the end Walls 31. A cross plate6! connects the end walls 31, 3'! and is vertically slotted as at 52.The baffle 68 has adjustment screws 53 extending horizontally therefromand passing through the slots 62 in plate 6|. Lock-nuts M are used toadjust the position of the bafile 50 relative to the discharge end ofthe hopper and also to control the clearance of the lower edge of thebafile 60 with respect to the casting plates passing thereunder.

In place of individual casting plates 23 the endless conveyor 20 mayhave a casting-surface or member carried directly thereon. Such acasting member will be in the form of an endless belt of flexiblematerial. The coated surface of this conveyor belt is smoothly polishedto provide an appropriate casting-surface which will hold the solutionduring the evaporation of the film.

Such a casting-surface may also be equipped as desired with flanges orledges upon its side edges which will operate similar to the guidestrips 3!! to hold the edge of the film while drying.

The operation of this device may be briefly described as the continuouspresentation to a discharge hopper of a casting-surface which may eitherbe continuous or in suitable removable sections. This casting-surface ormember is brought to uniform temperature with the solution and theconditions in chamber 33 so that the operation of evaporation of thesolvent will not be attended by undesirable efiects such as occur when acomposite film comes in contact with a plate of a different temperaturecausing a differential solidification and separation out of the film ofthat component which solidifies at a temperature lower than theremaining com.- ponents.

The casting plate 23 as it is advanced to the hopper is equipped withthe guide strips 3i) which prevent the lateral spread of the solutiondeposited.

The solution is discharged from the slot in the base of the hopper andbetween walls 37 and 38 and the panel 49. The rate of discharge isaccurately controlled by the adjustment of the dis.-

charge lips'50 and 5|. The solution on discharge spreads laterally into.contact with the guide strips 30 and drains downwardly to the baflle 60.The bafile 60 causes the solution to accumulate in a shallow pool, theupper surface of which extends slightly to the left of the lip 50 as:shown in Fig; 8,

Due to the upward slope of the casting plate 23 and its continuousmovement toward the upper end of the conveyor, there is a tendency forthe solution to flow in the opposite direction from that of the castingplate and to return to the pool. This action insures first, an adequatedeposit of the solution upon the casting plate regardless of variationin viscosity and immediately thereafter the draining of excess solutionto the pool so that the desired thinness of the film may be attained andits upper surface remain quite flat.

In the course of the travel of the plate together with the depositedfilm solution through the chamber 33, there is produced an evaporationof the solvent dependent upon the rate of travel, the temperaturemaintained and the surface tension or degree of saturation of thesolvent which is permitted to remain in the chamber. The film,therefore, dries or evaporates uniformly. There is no tendency for thesurface of the film to dry too fast and form a coating through which.the solvent cannot escape from U The film on reaching the discharge endof the chamber 33 will be sufficiently hardened to permit it to be cutinto sections defined by the size of the casting plates. The latter withthe film still adhering both to the plates and to the guide strips maythen be transferred to the conditioning chamber 34.

Where the conveyor itself carries the casting surface, the conveyor maybe extended to pass through the conditioning chamber 34 and thus carrythe film in a continuous: strip.

In like manner the chamber 34 may extend for sufficient distance topermit the use of a second or subsequent discharge hopper. Thus the filmdeposited from the first hopper may be partially or substantiallyevaporated and coated with a second film of the same or a different filmsolution and the composite film evaporated prior to reaching thedischarge point from the conveyor.

Through the procedure outlined above and by means of the machine asdescribed, provision is made for casting laminated sheets and strips incontinuous operation and for drying the sheets thoroughly betweensuccessive coatings. The firmness With which the films are held undertension on the surface of the casting element and the particularatmosphere of solvent vapors maintained reduces the likelihood ofsurface irregularities such as craters and pits. The accurate control-ofthe conditions of temperature permits the casting of pre-heatedsolutions at elevated temperatures and upon pre-heated casting surfaces.

The provision of the chamber of solvent vapors is of primary importanceas permitting the use of inexpensive low-boiling solvents in conjunctionwith inexpensive diluents. At the same time it is a great improvement inpreventing blushing which would be'otherwise caused by precipitation ofmoisture. It will also be evident that such a controlled atmosphereduring evaporation prevents surface-sealing and pin-holes.

By causing the solution to accumulate first in a pool of substantialdepth and in contact with the guide strips, the latter are thoroughlywet to form an edge contact with the film which remains throughout thesubsequent operations.

Where the solution contains oxidizing products, glycerol, phthalateresins or drying oils, which require baking or other heat treatment todry, the upwardly inclined travel through the heated chamber of solventvapors is of particular advantage. r

The mechanism above described will thus be seen to be suitable for thecontinuous production of films of various types and kinds. While oneparticular form of the device has been described, many variations instructural details and operation are comprised within the scope of theinven-- tion and as defined by and limited to the following claims. x

What I claim is:

1. The process of casting film in sheet or strip form which comprisesdepositing a film-forming solution uniformly over a casting surface,said casting surface having means to contact said filmforming solutionat the sides or edges thereby causing the sides or edges of thedeposited solution to be engaged and held against retraction,evaporating volatile solvent therefrom, said engagement beingmaintained-during evaporation of volatile solvent of the film-formingsolution to the extent that the film is held under tension and againstthe casting surface during and after the formation of said film.

2. The process of casting film which comprises flowing a film-formingsolution of suitable characteristics upon a casting surface, causing itsopposite edges to be anchored in proximity to the surface, evaporatingvolatile solvent therefrom, maintaining such engagement untilevaporation of volatile solvent has substantially ceased therefrom, andthen removing the film so produced.

3. ,The process of casting film which comprises depositing afilm-forming solution uniformly over a casting surface, said castingsurface having meansto contact said film-forming solution at itsopposite sides or edges, said means causing the sides or edges of thedeposited solution to-be engaged and securely anchored in proximity tosaid surface, evaporating volatile solvent therefrom and maintainingsaid anchorage during the evaporation of volatile solvent and formationof film.

4. The process of casting multi-layer composite films of predeterminedthickness which comprises depositing a known quantity of film-formingsolution uniformly over a casting surface, said casting surface havingmeans to contact film-forming solutions at opposite sides or edges andanchor said solutions and hold same in place without distortion duringthe evaporation of volatile solvent therefrom, uniformly depositingthereupon subsequent layer or layers comprising known quantities offilm-forming solutions, uniformly drying said composite film undertension and finally removing the substantially dry composite film fromthe casting surface.

5. The process of casting film which comprises depositing a film-formingsolution uniformly upon a fiat casting surface travelling in continuousmovement along an upward gradient opposite to the direction in which thesolution is first applied, within a regulated quiescent atmospherecomprising a regulated concentration of solvent vapors, partiallyevaporating volatile solvent from said film-forming solution within saidatmosphere, removing the forming film from said atmosphere anddepositing said film and said casting surface within a conditioningchamber, subjecting said film to evaporating media therein, and finallyremoving said film from said casting surface.

6. The process of casting film in sheet or strip form in continuousprogressive operation which comprises uniformly depositing upon a movingflat casting surface a film-forming solution con tained in a dischargehopper supported adjustably above and across said casting surface, saidcasting surface being adapted to travel in continuous movement along anupward gradient, draining excess solution to a pool, evaporatingvolatile solvent and then removing from the" casting surface the film soproduced.

7. In the process of forming films and evaporating volatile liquidsolvent therefrom steps comprising depositing a film forming solutionuniformly upon a casting surface within a relatively closed chambercomprising a quiescent atmosphere wherein the concentration of gaseoussolvent vapor is regulated as to the mass per unit volume, said castingsurface having means to contact said solution at its opposite sides oredges,

contacting said solution with said means to form attaching edges andcause said edges of said solution to be engaged and held againstretraction, subjecting said solution within said chamber to theinfluence of temperature and pressure adapted to convert liquid into itsvapor, subjecting said solution withinsaid chamber to the influence ofvapor saturated to a degree adapted to substantially regulate thetendency of said solution to form vapor, said vapor being saturatedsubstantially with the liquid from said-solution from which solutionsaid vapor is derived, evaporating volatile solvent from said solutionwithin said chamber to form a film engaged upon said casting surface,said engagement being maintained during the evaporation of volatilesolvent to the extent that the film is held under tension and againstthe casting surface during and after the formation of said film,uniformly intensifying the strength of said film while held undertension upon said casting surface within said chamber by a regulatedrate and a regulated degree of substantially uniform evaporation ofliquid from said film, removing said film upon said casting surface fromsaid chamber, depositing said film and said casting surface within aconditioning chamber, subjecting said film within said conditioningchamber to the influence of temperature and pressure adapted toevaporate substantially all volatile solvent remaining in said film andadapting said'film to receive subsequent coating or coatings of similaror dissimilar film forming substance.

8. In the process of forming films and evaporating volatile liquidsolvent therefrom steps comprising depositing a film forming solutionfrom a pool uniformly upon a fiat surface travelling in continuousmovement along a uniform upward gradient opposite to the direction inwhich the solution is first applied within a relatively closed chambercomprising a wherein the concentration of gaseous solvent vapor isregulated as to the mass per unit volume, said casting surface havingmeans to contact said solution at its opposite sides or edges,contacting said solution with said means to form attaching edges andcause said edges of said solution to be engaged and held againstretraction, draining excess solution to said pool, subjecting saidsolution within said chamber to the influence quiescent atmosphere oftemperature and pressure adapted to convert liquid into its vapor,subjecting said solution within said chamber to the infiuence of vaporsaturated to a degree adapted to substantially regulate the tendency ofsaid solution to form vapor, said vapor being saturated substantiallywith the liquid from said solution from which solution said vapor isderived, evaporating volatile solvent from said solution within saidchamber toform a film engaged upon said casting surface, said engagementbeing maintained during evaporation of volatile solvent to the extentthat the film is held under tension and against the casting surfaceduring and after the formation of said film, uniformly intensifying thestrength of said film while held under tension upon said casting surfacewithin said chamber by a regulated rate and a regulated degree ofsubstantially uniform evaporation of liquid from said film.

9. In the process of forming composite films and evaporating volatileliquid solvent therefrom steps comprising depositing a film formingsolution from a pool uniformly upon a flat casting surface travelling incontinuous movement along a uniform upward gradient oppositeto thedirection in which the solution is first applied within a relativelyclosed chamber comprising a quiescent atmosphere wherein theconcentration of gaseous solvent vapor is regulated as to the mass perunit volume, draining excess solution to said pool, evaporating volatilesolvent from said solution within said chamber to form a film upon saidcasting surface, depositing thereupon within said chamber a second filmforming solution to form a composite film, subjecting said solutionswithin said chamber to the influence of temperature and pressure adaptedto convert liquid into its vapor, subjecting said solutions within saidchamber to the influence of vapor saturated to a degree adapted tosubstantially regulate the tendency of said solutions to form vapor,said vapor being saturated substantially with the liquid from saidsolutions from which solution said vapor is derived, uniformlyintensifying the strength of said film upon said casting surface withinsaidchamber by a regulated rate and a regulated degree of substantiallyuniform removal of unneeded liquids from said film, removing saidcomposite film upon said casting surface from said chamber, depositinsaid film and said casting surface within a conditioning chamber,subjecting said film within said conditioning chamber to the influenceof temperature and pressure adapted. to evaporatesubstantially allvolatile solvent remaining in said. film, and

then removing said film from said casting surface.

10. The process of making multi-ply composite film, comprising uniformlyapplying one or more layers of film-forming material dissolved involatile solvent to an area of a film base layer on a casting surface,said base layer being firmly affixed at its opposite edges and securelyheld under tension against said casting surface, evaporating volatilesolvent, and removing the composite film so formed from said castingsurface.

11. The process of casting film which comprises flowing a film formingsolution of suitable characteristics upon a casting surface; causing itsopposite edges to be anchored in proximity to the surface; solidifyingsaid film forming solution to form a film; maintaining said edgeengagement until solidification has been substantially effected; andthen removing the film from the cast ing surface.

12. The process of casting film which comprises flowing a film formingsolution of suitable characteristics upon a casting surface; causing itsside edges to be anchored in proximity to the surface; solidifying saidfilm forming solution to form a film; maintaining said engagement of theside edges of the film until solidification has been substantiallyeffected; and then removing the film from the casting surface.

13. The process of casting film in sheet or strip form in continuousprogressive operation which comprises flowing a film forming solutionupon a casting surface moving in an upwardly inclined gradient; engagingthe edges of the film in proximity to the casting surface to hold saidfilm against retraction; removing solvent from the film forming solutionto solidify the film; and then removing the formed film from the castingsurface.

14. The process of forming composite film in sheet or strip form incontinuous progressive operation which comprises flowing a film formingsolution upon a casting surface moving in an up wardly inclinedgradient; engaging the edges of the film in proximity to the castingsurface to hold said film against retraction;- removing solvent from thefilm forming solution to solidify the film; flowing a second filmforming solution on said solidified film on said upwardly inclinedgradient; engaging the edges of the second deposited film to hold saidsecond deposited film against retraction; removing solvent from saidsecond deposited film forming solution to solidify the film; andremoving the composite film from the casting surface.

CLYDE SCOTT.

